It's a challenge indeed. IF you are running on fumes, it will be harder
for the automatic locking to find first and second modulations, and if
it does this, it is much more likely to be the central pedestal as the
others will be even further down into the noise. The lack of the
fundamental tone will cause that FLL may fail to lock, since the sweep
signal can be too strongs, and if it does lock, it will be weak as the
loop gain will be off by the lack of signal and then naturally the S/N
will be problematic.
Not sure that it in itself will be the cause of systematically drifting
of the mark, but rather varying a lot around that mark.
Cheers,
Magnus
On 12/06/2014 08:16 PM, paul swed wrote:
All good answers with a good tube and enough current to read on the meter.
But I am working at the very limit of the Cs fumes. There is current, about
.5 to 1 tick mark on the meter of a 5061 using a 5060 tube.
Thats the challenge on a very eol tube.
Regards
Paul.
On Sat, Dec 6, 2014 at 1:56 PM, Magnus Danielson <[email protected]
wrote:
Tom,
On 12/06/2014 06:04 PM, Tom Van Baak wrote:
Paul,
There are 7 peaks total, about 40 kHz apart (on my 5061A). If you're
talking about just the central peak, there are two smaller peaks on either
side, about 1 kHz apart. The exact value depends on internal magnetic
field, which is specific to each beam tube design.
For some measurements of all the peaks, have a look at:
http://leapsecond.com/pages/cspeak/
These are the 7 Zeeman pedestals, and on top of them you have the Ramsay
fringes. You can indeed lock onto the wrong Ramsey-fringe, but they too
have amplitude differences. For a normal tube, they are quite significant,
but if you look at the Ramsay fringes on the NIST-F1, they are much denser
and looses amplitude much slower, so you need to pay more details of which
fringe you use. The density of the Ramsay fringes is due to the observation
time, which has been one of the driving forces to develop hydrogen masers
and cesium fountains, but for a simple cesium tube, it's a few dm of
distance and the average speed of the cesium steam.
You can play with the C-field in addition to playing with peaks:
http://leapsecond.com/images/cfield.gif (578 x 4610 pixels)
Which is a good illustration. It would be good.
For more details search the archives for the word Zeeman. For example:
https://www.febo.com/pipermail/time-nuts/2005-April/018171.html
A nice description from hp how a cesium beam standard works:
http://leapsecond.com/museum/hp5062c/theory.htm
Do check the FTS-4065C manual as I just uploaded. Good complementary
information.
Cheers,
Magnus
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